The present invention relates to a gas delivery system that has the capability of cyclically delivering a selectable volume of gas at a predetermined rate for a predetermined interval, in a miniature, portable unit. More specifically, the gas delivery system will have primary and immediate utilization as a miniature respirator that can be worn by patients suffering from impaired lung function and that is also advantageous for inter-hospital and intra-hospital transport of patients requiring continuous ventilation.
The invention will have similar future application as a wearable driver for pneumatic total artificial hearts (TAH) as for patients with permanently implanted hearts and for those with hearts implanted as bridges prior to heart transplant.
Many patients with chronic respiratory failure due to a variety of pulmonary (and non-pulmonary) diseases require prolonged (or permanent) mechanically assisted ventilation for life support. Unfortunately, the majority of the patients must be cared for in the acute hospital setting, with its high attendant costs, and its interruption of the beneficial support structure of the home environment. In addition, conventional mechanical ventilators (of the volume-cycled type) are bulky, and expensive, and necessarily restrict the patient to a bed-chair existence. A small, wearable respirator has been developed that is a major advance for the management of such patients and it obviously has numerous applications outside the setting of chronic ventilator dependency. The current nationwide emphasis on medical cost containment is a highly supportive atmosphere for such a device which will clearly lead to the successful hospital discharge, and subsequent rehabilitation of many such patients. The pilot studies of Make et al (CHEST 86: 358-365, September 1984) from the Pulmonary Section at Boston University have clearly demonstrated a need for a portable volume ventilator (in their studies a relatively large wheelchair based Bio-Med IC-2 ventilator has been used).
The wearable respirator that has been developed offers clear-cut advantages in terms of size, weight, portability and versatility (with a wide range of respiratory rate, tidal volume, cycle pressures, and inspiratory/expiratory time options). These features have been noted to be very important, particularly in the management of patients with airways obstruction. While this approach to the management of ventilator-dependent patients in the hole is a relatively new departure for the United States, there are well-developed support programs that cater to the needs of hundreds of ventilator-dependent patients in England and France (Goldberg, AI, CHEST 86: 345, Sept. 1984). Once again, the development of a small wearable respirator is a very important adjunct to the advancement of such programs in the United States.
For those patients or conditions where a higher concentration of oxygen in the ventilating gas is required, the wearable respirator has provision for the addition of oxygen at a controlled rate from a wearable oxygen supply to provide an oxygen-rich mixture of a selected concentration.
Another very useful application for the miniature battery-powered respirator is in transporting patients who require chronic mechanical ventilatory support from one location to another, e.g. from one hospital to another, or from one location to another in the same hospital. In addition, the device can also be used to provide temporary respiratory support in an ambulance for patients with acute cardio-respiratory arrest or other forms of rapidly developing respiratory failure (smoke inhalation, chest trauma, etc.).
A miniature wearable air supply based on the new gas delivery means will be sufficiently small and light to be worn by ambulatory patients with planted, pneumatically operated Total Artificial Hearts (TAH), such as the Utah heart, the Philadelphia (Temple University) heart, made by Cardiac Systems, Inc., and the Jarvik heart, made by Symbion, Inc. A primary application for a wearable air supply with a pneumatic TAH is as a temporary replacement for patients awaiting transplants. A wearable air supply can also be useful with implanted, pneumatically-operated left ventricular assist devices, such as the Kantrowitz aortic patch (LVAD Technology). The weights of present portable driving systems are 15 pounds or more, for both the Heimes unit designed for use with the Utah or Technology unit, designed for use with the LVAD Technology Mechanical Auxiliary Ventricle Implant (aortic patch). The weight of the new air supply will be slightly over five pounds. It will permit mobility for a patient with a temporarily implanted TAH or LVAD awaiting a transplant, as well as mobility for an individual with a permanently implanted TAH or LVAD, in the home, for periods of between one and two hours. Such mobility cannot be provided with the relatively heavy portable units; and when the patient is away from home and using a portable unit, the wearable supply will provide necessary reliability and back-up in an emergency situation.